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RE: [Linux-cluster] GFS performance.



Hi,

I am using Virtuozzo OS visualization which does not have a single file for the entire VM's filesystem. All VMs are simply sub-directories and OS files are stored in a common templates directory which is sym linked to back to the VM's directory, so if an OS file is changed inside the VM then the symlink breaks and a new file is put in the VM's private directory. I cant use GFS2 because it is not supported by Virtuozzo. All VMs are simply running web/db/ftp.

So this basically means that there are a lot of symbolic links (small files). The GFS has a block size of 4K so I also chose 4K as my block size for my performance testing to asses the worst case scenario. If I change the block size to 256K then the performance difference between ext3 and GFS are minimal. Also when I migrate the VM out from GFS(RAID5 SAS 15K) to ext3(single disk SATA), there is a significant noticeable performance gain!

Below tests are on the same disk set (5 disk RAID5 SAS 15K) with 2 partitions, GFS and ext3.
Results at 4K random reads:
GFS : about 1500K/s
ext3 : about 7000K/s

Results at 256K random reads:
GFS : about 45000K/s
ext3 : about 50000K/s

Results at 256K sequential reads:
GFS : over 110,000K/s (my single GB NIC maxes out)
ext3 : over 110,000K/s (my single GB NIC maxes out)

fio test file as below only rw and blocksize were changed for the 3 different scenarios above.
[random-read1]
rw=randread
size=10240m
directory=/vz/tmp
ioengine=libaio
iodepth=16
direct=1
invalidate=1
blocksize=4k

[random-read2]
rw=randread
size=10240m
directory=/vz/tmp
ioengine=libaio
iodepth=16
direct=1
invalidate=1
blocksize=4k

Thanks,
Vikash.


At 01:00 AM 21-04-09, Jeff Sturm wrote:
> -----Original Message-----
> From: linux-cluster-bounces redhat com
> [mailto:linux-cluster-bounces redhat com] On Behalf Of Vikash
> Khatuwala
> Sent: Monday, April 20, 2009 11:23 AM
> To: linux-cluster redhat com
> Subject: [Linux-cluster] GFS performance.
>
> OS : CentOS 5.2
> FS : GFS

Can you easily install CentOS 5.3 and GFS2?  GFS2 claims to have some
performance improvements over GFS1.

> Now I need to make a decision to go with GFS or not, clearly
> at 4 times less performance we cannot afford it, also it
> doesn't sound right so would like to find out whats wrong.

Be careful with benchmarks, as they often do not give you a good
indication of real-world performance.

Are you more concerned with latency or throughput?  Any single read will
almost certainly take longer to complete over GFS than EXT3.  There's
simply more overhead involved with any cluster filesystem.  However,
that's not to say you're limited as to how many reads you can execute in
parallel.  So the overall number of reads you can perform in a given
time interval may not be 4x at all (are you running a parallel
benchmark?)

Jeff


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